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Mac OS, which stands for Macintosh Operating System, is a series of graphical user interface-based operating systems developed by Apple Computer for their Macintosh line of computer systems. The original Mac OS is often credited for popularizing the graphical user interface successfully. It was first introduced in 1984 with the original Macintosh, the Macintosh 128K.

Apple deliberately played down the existence of the operating system in the early years of the Macintosh to help make the machine appear more user-friendly and to distance it from other operating systems such as MS-DOS, which were portrayed as arcane and technically challenging. Apple wanted Macintosh to be portrayed as a system "for the rest of us". Therefore the term "Mac OS" didn't really exist until it was officially used during the mid-1990s. The term has since been applied to all versions of the Mac system software prior to this as a handy way to refer to it when discussing it in context with other operating systems.

Earlier versions of the Mac OS were compatible only with m68k-based Macintoshes, while later versions were also compatible with the PowerPC (PPC) architecture. Most recently, Mac OS X has become compatible with Intel's x86 architecture.

Versions

The Macintosh operating system initially consisted of two pieces of software, called "System" and "Finder", each with its own version number. They were bundled for upgrades as "System Software" with a single version number for each combination. This was formally shortened to "System" (and the component version numbers synchronised) with "System 6". System 7.5.1 was the first to include the Mac OS logo (a blue variation of a smiley face), and Mac OS 7.6 was the first to be named "Mac OS" (to ensure that users would still identify it with Apple, even when used in "clones" from other companies).

Until the advent of the later PowerPC G3-based systems, significant parts of the system were stored in physical ROM on the motherboard. The initial purpose of this was to avoid using up the limited storage of floppy disks on system support, given that the early Macs had no hard disk. (Only one model of Mac was ever actually bootable using the ROM alone, the 1991 Mac Classic model.) This architecture also helped to ensure that only Apple computers (and later licensed clones with the copyright-protected ROMs) could run Mac OS.

The Mac OS can be divided into two families of operating systems:

• "Classic" Mac OS, the system which shipped with the first Macintosh in 1984 and its descendants, culminating with Mac OS 9.
• The newer Mac OS X (the "X" is pronounced ten, as the Roman numeral). Mac OS X incorporates elements of OpenStep (thus also BSD Unix and Mach) and Mac OS 9. Its low-level BSD-based foundation, Darwin, is free software/open source software.

"Classic" Mac OS (1984-2001)

The "classic" Mac OS is characterized by its total lack of a command line; it is a completely graphical operating system. Heralded for its ease of use, it is also criticized for its singletasking (in early versions) or cooperative multitasking (in later versions), very limited memory management, lack of protected memory, and susceptibility to conflicts among "extensions" that extend the operating system, providing additional functionality (such as networking) or support for a particular device. Some extensions may not work properly together, or work only when loaded in a particular order. Troubleshooting Mac OS extensions can be a time-consuming process of trial and error.

Mac OS originally used the Macintosh File System (MFS), a flat file system with only one kludged level of folders. This was replaced by the Hierarchical File System (HFS), which had a true directory tree. Both file systems are otherwise compatible.

Most file systems used with DOS, Unix, or other operating systems treat a file as simply a sequence of bytes, requiring an application to know which bytes represented what type of information. By contrast, MFS and HFS gave files two different "forks". The data fork contained the same sort of information as other file systems, such as the text of a document or the bitmaps of an image file. The resource fork contained other structured data such as menu definitions, graphics, sounds, or code segments. A file might consist only of resources with an empty data fork, or only a data fork with no resource fork. A text file could contain its text in the data fork and styling information in the resource fork, so that an application which didn't recognize the styling information could still read the raw text. On the other hand, these forks provided a challenge to interoperability with other operating systems; copying a file from a Mac to a non-Mac system would strip it of its resource fork.

The Classic OS is still supported and shipped in addition to OS X with PowerPC (but not Intel) Macs as late as early 2006.

Mac OS X (2001-present)

Mac OS X brought Unix-style memory management and pre-emptive multitasking to the Mac platform. It is based on the Mach kernel and the BSD implementation of UNIX, which were incorporated into NeXTSTEP, the object-oriented operating system developed by Steve Jobs' NeXT company. The new memory management system allowed more programs to run at once and virtually eliminated the possibility of one program crashing another. It is also the second Macintosh operating system to include a command line (the first is the now-discontinued A/UX, which supported classic Mac OS applications on top of a UNIX kernel), although it is never seen unless the user launches a terminal emulator.

However, since these new features put higher demands on system resources, Mac OS X only officially supported the PowerPC G3 and newer processors, and now has even higher requirements (the additional requirement of built-in FireWire (IEEE 1394), as of Mac OS X v10.4). Even then, it runs somewhat slowly on older G3 systems for many purposes.

As of 2005, every update to Mac OS X since the original public beta has had the atypical quality of being perceptibly more responsive than the version it replaced, the opposite to the trend of most operating systems. As noted by John Siracusa of Ars Technica:

"For over three years now, Mac OS X has gotten faster with every release—and not just "faster in the experience of most end users", but faster on the same hardware. This trend is unheard of among contemporary desktop operating systems."

This could, however, be attributed to the relative immaturity of the OS, and the speed gains have diminished as OS X has matured. Some reports regarding Mac OS X 10.4 suggested that it seemed similar to version 10.3 in responsiveness, or even slower at times.

Power PC builds of Mac OS X includes a compatibility layer for running older Mac applications, the Classic Environment. This runs a full copy of the older Mac OS, version 9.1 or later, in a Mac OS X process. PowerPC based Macs ship with OS 9.2 as well as OS X. OS 9.2 must be installed by the user-- it is not installed by default (as of early 2006). The Classic Environment does not work in the x86 version of OS X. Most well-written "classic" applications function properly under this environment, but compatibility is only assured if the software was written to be unaware of the actual hardware, and to interact solely with the operating system.

Users of the original Mac OS generally upgraded to Mac OS X, but a few criticized it as being more difficult and less user-friendly than the original Mac OS, for the lack of certain features that had not been re-implemented in the new OS, or for being slower on the same hardware (especially older hardware), or other, sometimes serious incompatibilities with the older OS. Because drivers (for printers, scanners, tablets, etc.) written for the older Mac OS are not compatible with Mac OS X, and due to the lack of OS X support for older Apple machines, a significant number of Macintosh users have continued using the older OS. By 2005, it is reported that almost all users of systems capable of running Mac OS X are so doing, with only a small percentage still running the classic Mac OS.

In June 2005, Steve Jobs announced at his Worldwide Developers Conference keynote that Apple computers would be transitioning from PowerPC to Intel processors. At the same conference, Jobs announced Developer Transition Kits that included beta versions of Apple software including Mac OS X that developers could use to test their applications as they ported them to run on Intel-powered Macs. In January 2006, Apple released the first Macintosh computers with Intel processors, an iMac and the MacBook Pro, and in February 2006, Apple released a Mac Mini with an Intel Core Solo and Duo processor.

"Classic" Mac OS technologies

Some features of the "classic" Mac OS are still in use in Mac OS X, including:

ColorSync

ColorSync is a technology for matching colors between the screen and a printer.

Finder

The Finder is the interface for browsing the filesystem and launching applications.

MacRoman

MacRoman is the character encoding used in classic Macintosh systems. Mac OS X's standard character encoding is Unicode, in its UTF-8 and UTF-16 forms, but HFS volumes using MacRoman encoding are still supported.

PlainTalk

PlainTalk is a speech synthesis and speech recognition technology. It is still a part of the Macintosh operating system, although the proprietary microphone interface bearing the same name was phased out with the introduction of the Blue and White PowerMac G3s in 1999.

QuickDraw

QuickDraw was the first imaging model to provide mass-market WYSIWYG capabilities. Although mostly obsolete on Mac OS X, due to the use of Quartz, QuickDraw still works on Mac OS X 10.4.

QuickTime

QuickTime provides support for audio-visual playback.

Obsolete technologies

Many technologies of the "classic" Mac OS are no longer used on OS X, including:

Chooser

The Chooser is a tool for enabling AppleTalk, and accessing and selecting network resources such as printers. It was derived from the Choose Printer Desk Accessory found in early version of the Mac OS.

Desk Accessories

Desk Accessories were small "helper" applications that could be run concurrently with other applications, prior to the advent of the multi-tasking MultiFinder and System 7. They have not been used in the Mac OS since System 7.

Mac OS memory management

This term describes how the Macintosh managed RAM and virtual memory before the switch to the Unix-based Mac OS X. It has been defunct since Mac OS X, but most of the APIs are still available via the Carbon compatibility layer.

MultiFinder

MultiFinder was a version of the Finder with support for simultaneous processes. It became a part of the Finder in System 7.

PowerPC emulation of the Motorola 68000

This refers to the way in which the Macintosh handled the architectural transition to the PowerPC microprocessor. This has been obsolete since Mac OS X, as Mac OS X only runs software built for the PowerPC; however, a similar emulation technology is seen in Rosetta, which allows an Intel-based Macintosh to emulate software built for PowerPC-based Macintoshes.

Project Star Trek

One interesting historical aspect of the classic Mac OS was a relatively unknown secret prototype Apple started work on in 1992, code-named Project Star Trek. The goal of this project was to create a version of Mac OS that would run on Intel-compatible x86 personal computers. It was short lived, being cancelled only one year later in 1993 due to political infighting, though its team was able to get the Macintosh Finder and some basic applications, like QuickTime, running smoothly on a PC.

Although the Star Trek software was never released, third-party Macintosh emulators, such as vMac, Basilisk II, and Executor, eventually made it possible to run the classic Mac OS on Intel-based PCs. These emulators were restricted to emulating the 68000 series of processors, and as such couldn't run versions of the Mac OS that succeeded 8.1, which required PowerPC processors. Recently, the PearPC emulator has appeared, which is capable of emulating the PowerPC processors required by newer versions of the Mac OS (like Mac OS X). Unfortunately, it is still in the early stages and, like many emulators, tends to run much slower than a native OS would.

Another PPC emulator is SheepShaver, which has been around since 1998 for the BeOS platform, but in 2002 was open sourced with porting efforts beginning to get it to run on other platforms. Although it is capable of emulating a PowerPC processor, it can only emulate up to Mac OS 9.0.4 because it does not emulate a memory management unit.

Of course, it is interesting to note that 16 years after project Star Trek, the current version of Mac OS (v10.4.4) runs smoothly on x86 architecture, since the iMac, MacBook Pro, and Mac Mini are built around Intel chips. The iMac, MacBook pro and Mac Mini are the first three models of a complete Apple switch to x86 architecture (see also Project Marklar below).

Project Marklar

In April 2002, eWeek reported a rumor that Apple had a version of Mac OS X running on x86 processors, code-named Marklar. The idea behind Marklar was to keep Mac OS X running on an alternate platform should Apple become dissatisfied with the progress of the PowerPC platform. These rumors subsided until late in May 2005, when CNet reported that Apple would unveil Marklar in the coming months. The rumor was confirmed by Apple's CEO Steve Jobs in June 2005, when he announced that future Macintosh products will run on Intel processors starting in 2006. After pre-release x86-based Macs were released to developers, a copy of the x86-based version of Mac OS X was leaked onto the Internet, and hackers managed to get it to run on non-Apple x86-based PCs.

Apple's plans to fully port Mac OS X from IBM's PowerPC processors to Intel's x86 processors include Rosetta, which translates PowerPC instructions to x86 instructions. For applications in active development, Apple's latest version of Xcode permits an application to be built for both the PowerPC and Intel processors simultaneously. These "universal binaries" are similar to making a "fat binary" in the mid-1990's, which would hold both "680x0" and PowerPC instructions during Apple's transition to the PowerPC architecture.

Mac OS X for the x86 architecture requires an Intel Pentium 4, Intel Core, or AMD Athlon 64 processor, as it utilizes SSE, SSE2, and SSE3 instructions. Mac OS X x86 was first available for sale in the Apple Store in January 2006. It cost $1299 for an iMac, and $1999 for the newly introduced MacBook Pro.

Translation emulation and Macintosh clones

Some computers have been shown to successfully run Mac OS using the process of translation emulation. One example of this is the Amiga that successfully ran classic Mac OS using translation emulation for either the m68k or PowerPC processors. Example emulators include ShapeShifter (by the same programmer that conceived SheepShaver, Christian Bauer, not to be confused with the third party preference pane ShapeShifter), Fusion and iFusion. (The latter ran classic Mac OS using translation emulation with a PowerPC "coprocessor" accelerator card.) This form of emulation has been said to equal or better the speed of a Macintosh with the same processor, especially with respect to the m68k series due to real Macs running in MMU trap mode, hampering performance.

With the introduction of Intel Macs, it has been speculated that Mac OS could be run by a Intel (or compatible) PC via translation emulation but this has yet to be demonstrated and is strongly opposed by Apple.

Several computer manufacturers over the years have made Macintosh clones capable of running Mac OS, notably Power Computing and Umax. These machines normally ran various versions of Classic Mac OS. Steve Jobs ended the clone licensing program after returning to Apple in 1997.

A/UX

In 1988, Apple released its first UNIX based OS, named A/UX.

This was an operating system that seamlessly integrated the Mac OS look and feel with the power and flexibility of UNIX. Since it was before the advent of PowerPC and therefore had to run on the Motorola 68000 processor, it was not very competitive for its time. A/UX had most of its success in sales to the Federal government of the United States, where UNIX was a requirement that Mac OS could not meet.

See also

• Mac OS history
• Mac OS X history
• Mac OS X Server
• List of Macintosh software
• Operating system advocacy
• Comparison of operating systems

External links

• folklore.org a site with anecdotes by the creators of the first Macintosh
• Mac OS X official site

v t e Operating systems by Apple
Apple II, III, Lisa	Apple II Apple DOS ProDOS GS/OS Apple III SOS Lisa Lisa OS MacWorks
Mac	Classic Mac OS System 1 Systems 2, 3, and 4 System 5 System 6 System 7 Mac OS 8 Mac OS 9 macOS History NeXTSTEP OpenStep Rhapsody Public Beta Core Darwin XNU Desktop Mac OS X Public Beta 10.0 (Cheetah) 10.1 (Puma) 10.2 Jaguar 10.3 Panther 10.4 Tiger 10.5 Leopard 10.6 Snow Leopard 10.7 Lion OS X 10.8 Mountain Lion 10.9 Mavericks 10.10 Yosemite 10.11 El Capitan macOS 10.12 Sierra 10.13 High Sierra 10.14 Mojave 10.15 Catalina 11 Big Sur 12 Monterey 13 Ventura 14 Sonoma 15 Sequoia Server Mac OS X Server 1.0 Other projects Shipped A/ROSE A/UX AIX for Apple Network Servers MAE MkLinux PowerOpen Environment Cancelled Star Trek Taligent Copland Nukernel Vanguard
iOS derivatives	iOS iPhone OS 1 2 3 iOS 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 iPadOS 13 14 15 16 17 18 Others tvOS Apple TV Software visionOS watchOS audioOS bridgeOS
Others	Newton OS iPod software
List • Category

• Apple software
• Mac OS
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